I read an article about the roller coaster derailed

Subject:Mechanical EngineeringPrice: Bought3

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I read an article about the roller coaster derailed. Investigators determined that the sharp descent in the helical twist placed high side loads on the

wheel mechanisms. They found that the outside track wheel assembly was bent 30° from its normal vertical orientation; this was due to bending of the support bracket rail that connected the wheels to the underside of the car. 

Some people told me the reasons why the car derailed was it was bigger from the previous one and made many loops and turns; however, the support bracket rail was not redesigned from the previous car. Also,  The wheel assembly could disengage from the track if the support bracket rail is bent. The car indicated higher expected side loads on the wheel assembly and support bracket rail than the previous design. Because of the higher

expected loads, a stronger support bracket rail was needed and made out of a higher strength material. The dimensions of the support bracket rail were not changed from the previous design, so as to avoid a redesign of other portions of the car. Furthermore, In the previous design, the support bracket rails were made of low carbon steel (1018 steel); the material specifications called for the finished rails to have a Rockwell B-scale hardness between HRB 75 - HRB 85. For the new design, medium carbon steel (4130 steel) was used. The process involved heating to 844°C for 1 hour followed by water quenching, then post-quench tempering for 1 hour at 480°C. Parts were then cleaned of surface scale by grit blasting. The material specifications called for a final hardness of at least HRB 110. The designers say they have rechecked the loading calculations and claim that the wheel assembly and support bracket rail should be safe under the maximum expected loads plus a design margin (provided the rail material is at least 0.40 wt% carbon and the rail received the specified heat treatment)

Is that true these are the reason causing the car to derail? and Why?